1. Field of the Invention
The present invention relates to a coordinate input device utilizing ultrasonic waves for designating a position on a screen and inputting a locus of writing characters, graphics or the like in a computer system.
2. Description of the Related Arts
As a coordinate input device for designating a position on a screen of a computer, and inputting a locus of writing characters, graphics, or the like, the coordinates input devices utilizing various principles have been proposed. The coordinate input device utilizing ultrasonic waves among them generates ultrasonic waves from an input pen, receives the ultrasonic waves by a plurality of receivers, acquires a distance of the plurality of receivers and the input pen from an ultrasonic propagation time required from the input pen to the receivers and an ultrasonic speed, calculates the coordinate of the input pen, and inputs it into a computer.
In such the coordinate input device utilizing ultrasonic waves, a special configuration is not required to provide on an input plane unlike a touch panel of a resistive film system or an electromagnetic induction-type, and it is possible to input coordinates from various input planes such as a display screen of the computer, or a paper on a desk, a black board, or the like.
The proposed coordinate input device utilizing ultrasonic waves is provided with at least two receivers on the input plane, receives ultrasonic waves transmitted from the input pen in the input plane in synchronism with a certain synchronous signal by the two receivers, and acquires a coordinate in the input plane from each distance. Accordingly, it is necessary that the two receivers are provided on the input planes, respectively.
Furthermore, for example, as described in Japanese Patent Application Laid-Open No. 9-179684 (laid open on Jul. 11, 1997), three ultrasonic receivers are in common provided, to detect a coordinate value in a three-dimensional space of the input pen, so that the coordinate is input by distinguishing inputs from a plurality of input planes, respectively. This coordinate input device utilizing ultrasonic waves allows to input coordinates from arbitrary input plane.
However, the aforementioned coordinate input device utilizing ultrasonic waves requires three ultrasonic receivers in order to permit inputs from the plurality of input planes positioned in the three-dimensional space. In the aforementioned prior art, in order to allow the coordinate input from various input planes, it is necessary to provide the three ultrasonic receivers and a receiving circuit for detecting a propagation time of respective reception waves, thereby causing to increase cost.
The inventors studied hard, and it has become clear that a demand for inputting coordinates from various input planes is not so high, and that if it is possible to input coordinates from the input planes determined to a certain degree such as an already provided black board, an already provided desk, a display screen of a computer, or the like, the demand can sufficiently be satisfied.
It is therefore the object of the present invention to provide a coordinate input apparatus which is able to input coordinates from a plurality of input planes only by two ultrasonic receivers.
In order to attain the above object, according to an aspect of the present invention there is provided a coordinate input apparatus capable of making a coordinate input from a plurality of input planes, comprising an input device having an ultrasonic transmitter; two ultrasonic receivers which are aligned in a direction not perpendicular to the plurality of input planes and receives ultrasonic waves transmitted from the ultrasonic transmitter; a synchronizing means for synchronizing the input device with the ultrasonic receiver; an input plane setting part for setting a positional relation between the two ultrasonic receivers and the plurality of input planes; and an input coordinate generator which generates each distance from the input device to the two ultrasonic receivers in accordance with a propagation time interval from the input device to the two ultrasonic receivers of an ultrasonic signal to be received by the two ultrasonic receivers, and generates input coordinates in a plurality of the set input planes in accordance with the corresponding two distances.
According to the present invention, the two ultrasonic receivers are provided in common for the plurality of input planes, and further the plurality of input planes are restricted to a plane not perpendicular to a line connecting the two ultrasonic receivers, so that the sufficiently practicable coordinate input device can be provided. This is because when the line connecting the two ultrasonic receivers is perpendicular to the input plane, the distances from the input device in the input plane to the two ultrasonic receivers exist in a plurality of sets, so that the coordinates of an input device cannot be specified.
Furthermore, according to the present invention, in order to acquire the coordinates of the input device in the input plane by the two ultrasonic receivers, a positional relations between the two ultrasonic receivers and the plurality of input planes are made initial setting in advance. When this positional relations have been in advance set, it is possible to acquire the position of the input devices in the plurality of input planes from the distance from the input device to the two ultrasonic receivers.
According to the preferred embodiment, such the setting is made as the initial value setting prior to using the coordinate input device, and the initial value is recorded as a set value in a memory of the computer. For example, a three-dimensional coordinate in which the input plane is set as a two-dimensional coordinate plane and a direction perpendicular to the input plane is set as a third axis of coordinates is established, and coordinate values of the two ultrasonic receivers in such a three-dimensional coordinate system are made initial setting in each input plane. The coordinate values of the two ultrasonic receivers in the three-dimensional coordinate system of the respective input planes are established, so that the coordinate value of the input device in the input plane can be acquired from the distances between the input device and the two ultrasonic receivers.
According to the preferred embodiment, positions of the plurality of input planes are set so that the distances of the two ultrasonic receivers and the input planes differ among the plurality of input planes. A range of the respective input plane is initially set in each three-dimensional coordinate system, and then it is checked whether or not the coordinate value of the input device is in the range of the input planes which were initially set, so that it is possible to detect from which input plane the coordinate input is to be made.
In order to attain the above object, according to another aspect of the present invention there is provided a coordinate input apparatus capable of making a coordinate input from a plurality of input planes, comprising an input device having an ultrasonic transmitter (receiver); two ultrasonic receivers (transmitters) which are aligned in a direction not perpendicular to the plurality of input planes and receive (transmit) ultrasonic waves from (to) the ultrasonic transmitter (receiver); a synchronizing means for synchronizing the input device with the ultrasonic receivers (transmitters); an input plane setting part for setting a positional relation between the two ultrasonic receivers (transmitters) and the plurality of input planes; and an input coordinate generator which generates each distance from the input device to the two ultrasonic receivers (transmitters) in accordance with propagation time intervals from the input device to the two ultrasonic receivers (transmitters) of an ultrasonic signal to be received by the ultrasonic receivers, and generates input coordinates in a plurality of the set input planes in accordance with the corresponding two distances.
In a more preferred embodiment of the above invention, the input plane setting part sets coordinate values of the two ultrasonic receivers (transmitters) with respect to each of the plurality of input planes, in a three-dimensional coordinate system when a two-dimensional coordinate (X, Y) is taken on the input plane and a third coordinate axis (Z) is taken in a direction perpendicular to the corresponding input plane, and the input coordinate generator generates coordinate values of the input device in the three-dimensional coordinate system in accordance with the two distances.